In such an apparatus, for obvious reasons of convenience, the recirculation air inlet, like the outlets through which air is admitted into the cabin, is generally placed in the front of the cabin. A much reduced, or even non-existent, air flow in the rear region of the cabin can result from this. In addition, when the outside temperature is either very high or very low, the floor of the vehicle which is directly in contact with the outside atmosphere, and which is exposed in the first case to thermal radiation from the road surface, is itself brought to a high or low temperature, which in either case leads to discomfort for the occupants of the cabin whose feet rest on the floor.